Abstract：Hollow columns were made with sand-cement grout as test samples，on which the failure characteristic was studied in the condition of tri axis hydraulic fracturing. The samples were tested on tri axis seepage-stress coupled test apparatus. The data from test show that the stress states did not meet the failure criterion when samples failure. That phenomenon was studied in detail. The result that it was the asymmetry of the sample material leads to the stress field asymmetry. And local high stress can make sample failure from the local spot. Then stress concerctration happened in the failure spot，which focused on the fracture tip. And then the fracture development was induced. Finally the sample damaged entirely. A new concept，inhomogeneous coefficient，was set up to be used to describe the phenomenon of brittle materials failure in low stress level. For any brittle materials，the larger the inhomogeneous coefficient is，the larger the possibility of failure in low stress level is.
